Deeply dyed polyester fabric

ABSTRACT

A deeply dyed polyester fabric exhibiting a lightness index L* value of 25 to 60. Fibers at least in the surface layer portion of either or both of the warps and wefts exhibit a light transmittance to an extent such that the difference ΔX (%) between the light transmittance X⊥ (%) of polarized light vibrating perpendicular to the fiber axis at a wavelength of the maximum absorption and the light transmittance X .sup.[ (%) of polarized light vibrating parallel to the fiber axis at the same wavelength is not larger than 10%.

TECHNICAL FIELD

This invention relates to a dyed polyester fabric having a good colordepth, which is comparable to or superior to those of fabrics of naturalfibers.

By the term "good color depth" used herein, we mean that the fabric isdyed not only deeply but also with an enhanced brilliancy, i.e., deeplydyed without turbidity and light-brownish coloration.

BACKGROUND ART

Recently, the characteristics of polyester fibers have been remarkablyimproved. Especially, feeling, touch and drape of polyester fabrics havebeen improved to a level comparable to that of natural fibers (forexample, Japanese Examined Patent Publication No. 61-36099).Nevertheless, appearance, particularly the color depth, of the dyedpolyester fabrics is not attractive as compared with those of fabrics ofnatural fibers such as silk and wool. It is therefore usual thatconsumers' interest is not excited at the first sight, even though thefeeling and other characteristics are improved.

Proposals of improving the dyeability and other dyeing properties haveheretofore been made, which include, for example, the copolymerizationof a specific comonomer to effect relaxation of the fibrous structure(Japanese Examined Patent Publication No. 63-39686) and the formation ofmicropores in the surface portion of the fiber to effect diffusedreflection (Japanese Examined Patent Publication No. 62-28229). However,dyed polyester fabrics made by these proposals are still notsatisfactory in the color depth which term is used in a broad sense inthe present specification, i.e., in the color depth with brilliancy,although they are dyed deeply.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a dyed polyester fabricexhibiting a good color depth which is comparable or superior to thoseof natural fiber fabrics, as well as a good feeling, touch and drape.

In accordance with the present invention, there is provided a dyedpolyester fabric composed of warps and wefts, which are dyed with alightness index L* value of 25 to 65; fibers at least in the surfacelayer portion of either or both of the weft and the warp exhibiting alight transmittance to an extent such that the difference (ΔX in %)between the light transmittance (X⊥ in %) of polarized light vibratingperpendicular to the fiber axis at a wavelength of the maximumabsorption and the light transmittance (X.sup.[ in %) of polarized lightvibrating parallel to the fiber axis at the same wavelength is notlarger than 10%.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows graphs of light transmittances of fibers in the surfacelayer portion of the yarn constituting an example of the dyed polyesterfabric of the present invention;

FIG. 2 shows graphs of light transmittances of fibers of a conventionaldyed polyester fabric having an improved feeling;

FIG. 3 is a diagram illustrating the vibrating plane of natural light;

FIG. 4 is a diagram illustrating a principle of color development;

FIG. 5 is a diagram illustrating a light transmittance (A) of polarizedlight having a vibrating plane parallel to the fiber axis, and a lighttransmittance (B) of polarized light having a vibrating planeperpendicular to the fiber axis;

FIG. 6 is a diagram illustrating the state wherein dye molecules aredistributed in a random manner within a polyester fiber and thus thevibrating planes of natural light which are distributed in alldirections are absorbed;

FIG. 7 is a diagram illustrating the state where dye molecules areoriented in one direction within a polyester fiber and thus only onevibrating plane of natural light which is oriented in one direction isabsorbed; and

FIGS. 9 through 30 show graphs of light transmittances of fibers in thesurface layer portions of the yarns of the dyed polyester fabrics madein Examples 1 through 8 and Comparative Examples 1 through 5, describedbelow.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is graphs of light transmittances of polarized light throughfibers in the surface layer portion of the warp and/or weft constitutingthe dyed polyester fabric of the invention, wherein the ordinate and theabscissa denote light transmittance (%) and wavelength (nm),respectively.

In FIG. 1, curve A (solid line) shows a light transmittance of polarizedlight vibrating parallel to the fiber axis, and curve B (broken line)shows a light transmittance of polarized light vibrating perpendicularto the fiber axis.

In FIG. 1, the graphs are characterized in that there is no substantialdifference between the light transmittance (X.sup.[ %) (curve A) ofpolarized light vibrating parallel to the fiber axis at a wavelength (λ₀nm) of the maximum absorption and the light transmittance (X⊥ %) (curveB) of polarized light vibrating perpendicular to the fiber axis at thesame wavelength (λ₀ nm), and further that, in the other wavelengthregions, there is no great difference between the light transmittance(X.sup.[) (curve A) of polarized light vibrating parallel to the fiberaxis and the light transmittance (X⊥) of polarized light vibratingperpendicular to the fiber axis. Only when the difference (ΔX) betweenthe two light transmittances X.sup.[ and X⊥ of polarized light at awavelength of the maximum absorption is not more than 10%, i.e.,

    ΔX=X⊥-X.sup.[≦10%,

the polyester fabric exhibits a satisfactorily enhanced color depthwithout light-brownish coloration.

FIG. 2 shows graphs of light transmittances X.sup.[ and X⊥ of polarizedlight vibrating parallel and perpendicular to the fiber axis,respectively, through fibers in a conventional dyed polyester fabrichaving an improved feeling. In contrast to the graphs shown in FIG. 1,the difference ΔX in the two light transmittances X⊥ and X.sup.[ islarger than 20% at a wavelength (λ₀) of the maximum absorption and isalso large in most of the other wavelength region. When the differenceΔX between the two light transmittances X⊥ and X.sup.[ are large, theabsorption of light is insufficient and white light is found in thelight of the developed color, with the result that the developed coloris not satisfactory.

Before going into detailed explanation of the dyed polyester fabric ofthe invention, our fundamental view on the principle of colordevelopment by a dye will be described to facilitate the understandingof the invention.

When a polyester fiber is dyed with a dye, the color development occursdue to light absorption by the dye penetrated into the fiber. Theinventors have conducted researches as to how the light penetrated inthe fiber is capable of absorbing light sufficiently to develop a deepcolor with brilliancy.

Light is an electromagnetic wave which is a kind of transverse waves,and, as diagrammatically shown in FIG. 3, natural light (1) hasvibrating planes distributed in all directions. It is to be noted that,as diagrammatically shown in FIG. 4, color development by a dye occursin the case where a vibrating plane (1') of light is in agreement withthe bonding direction of the conjugated double bond (3) in the dyemolecule (2), light having a wavelength of the vibrating plane isabsorbed. It is considered that the best step for obtaining the intendedcolor depth lies in absorption of the entire vibrating planes of naturallight which are distributed in all directions. That is,.if part of thevibrating planes remains unabsorbed, the color developed by the absorbedlight contains white light and the developed color containslight-brownish color to some extent and thus the color depth is poor.

The inventors have determined the proportion of the quantity of thevibrating planes absorbed and that of the vibrating planes unabsorbed infibers of a conventional dyed polyester fabric having an improvedfeeling. This determination is carried out by a procedure wherein thevibrating planes of all directions are divided into a plurality of pairseach comprising two vibrating planes perpendicular to each other byusing polarizing plates (4, 4'), and the quantities of the dividedperpendicular vibrating planes are measured on the fiber (5) of theconventional dyed polyester fabric.

As the results, it has been found that, as shown in an example of FIG.2, the light transmittance (B) of polarized light vibratingperpendicular to the fiber axis is considerably larger than that (A) ofpolarized light vibrating parallel to the fiber axis, i.e., theabsorption of the vibration of electromagnetic waves of the former issmaller than that of the latter. Obviously, there is a great differencein absorption between the two kinds of polarized light.

If dye molecules (6) are distributed in a random state such that themolecules are oriented in all directions, as shown in FIG. 6, theconjugated double bonds of the dye molecules are also oriented in alldirections, and therefore, the vibrating planes of natural lightoriented in all directions are entirely absorbed and thus a brilliantand deep color is developed. In contrast, if the dye molecules (6) aredistributed in a state such that the molecules are oriented in onedirection, as shown in FIG. 7, and there is a great difference betweenthe light transmittance (X.sup.[) of polarized light vibrating parallelto the fiber axis and that (X⊥) of polarized light vibratingperpendicular to the fiber axis, then only one vibration of light ((a)in FIG. 7) is absorbed and the other vibrations of light pass throughthe fiber, and thus, the resulting developed color has a reduced colordepth and looks somewhat darkish and light-brownish.

The inventors have further examined the relationship of theabove-mentioned difference in the absorption of vibrating planes ofelectromagnetic waves with the visual color depth in various kinds ofdyed polyester fabrics. The results obtained are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                        Run No.                                                                              ΔX (%)                                                                           Y      Dyed Yarns                                             ______________________________________                                        1      30       1      Conventional silky blended yarn                        2      27       2      Yarn having multiplicity of ultra-                                            micro-pores in the surface portions                    3      33       3      Yarn modified with a metal sulfonate                                          group                                                  4      17       5      Blended yarn containing a lowly-                                              oriented fibers                                        5      14       5      Readily dyeable yarn spun at a ultra-                                         high spinning speed                                    6       5       8      Trial run yarn (1)                                     7       3       10     Trial run yarn (2)                                     ______________________________________                                         Note: Details of the dyed yarns listed in Table 1 are given in the workin     examples, below.                                                         

In Table 1, ΔX (%) denotes the difference between the lighttransmittance (X⊥) of polarized light vibrating perpendicular to thefiber axis at a wavelength of the maximum absorption and the lighttransmittance (X.sup.[) of polarized light vibrating parallel to thefiber axis,

    ΔX(%)=X⊥-X.sup.[.

Y (class) denotes color depth expressed by 10 rating visual organoleptictest and provided that the color depth of silk is class 7. Numericalvalues "10" and "1" means the largest color depth and the smallest colordepth, respectively.

As seen from the above results, the magnitude of the difference (ΔX)between the two light transmittances (X⊥) and (X.sup.[) of polarizedlight vibrating perpendicular and parallel, respectively, to the fiberaxis has a clear and close relationship with the visual color depth (Y).The smaller the ΔX value, the better the Y value.

In fact, the dyed polyester fabric of the present invention ischaracterized as exhibiting an extremely small ΔX value, i.e., asurprisingly enhanced visual color depth Y, as compared with theconventional yarns, even though there is no difference in the amount ofdye used between the yarn of the fabric of the present invention and theconventional yarns. When the difference (ΔX) between the lighttransmittance (X⊥ in %) of polarized light vibrating perpendicular tothe fiber axis and the light transmittance (X.sup.[ in %) of polarizedlight vibrating parallel to the fiber axis is not larger than 10% asdefined in the present invention, a dyed polyester fabric having a colordepth of a level exceeding the color depth of silk (Y=class 7 as shownin Table 1) is obtained. The dyed polyester fabric having such a highcolor depth have heretofore not obtained from the conventional polyesterfibers.

The dyed polyester fabric of the present invention characterized asexhibiting the above-mentioned enhanced color depth is made by a processwherein a polyester yarn having a specific structure is used as the warpand/or the weft and a specific dye is used for dyeing the yarns or thewoven fabric.

Ordinary polyester fibers have a dense structure and exhibit a highcrystallinity, and therefore, when dyed, the dye penetrates intonon-crystalline regions of the fibers. However, even in thenon-crystalline regions, the polyester molecules are oriented althoughto a minor extent, and therefore, the dye molecules are oriented to someextent in the direction parallel to the fiber axis as illustrated inFIG. 7, with the result that vibrating planes of electromagnetic wavesparallel to the fiber axis are absorbed, but vibrating planes thereofperpendicular to the fiber axis are absorbed only to a limited extent.Thus, a great difference arises between the transmittance of the planesvibrating parallel to the fiber axis and the transmittance of the planesvibrating perpendicular to the fiber axis, and undesirablelight-brownish coloration is caused.

To prevent the above-mentioned orientation of dye molecules and obtainthe state wherein the dye molecules are oriented randomly in alldirections as illustrated in FIG. 6, polyester fibers wherein thepolyester molecules are not oriented at all or oriented only to anegligible extent must be used. Typical examples of such polyesterfibers are (i) undrawn fibers which have been made by carrying out thefiber spinning at a spinning speed of 1,000 to 2,000 m/min and have notbeen subjected to a drawing step, and (ii) fibers which have been madeby carrying out the fiber spinning at a spinning speed higher than 2,000m/min but not higher than 5,000 m/min and heat-treating the spun fibersat a temperature of at least 220° C. under relaxed conditions to therebycompletely relax the polymer molecules in the non-crystalline regions.When such polyester fibers are made, at least one of the following stepscan be additionally employed: a step of melt-spinning the polymer at atemperature higher than 300° C. at orifices of a spinneret, a step ofspinning the polymer at a high spinning draft ratio of at least 1,000,and a step of employing a copolyester having copolymerized therein amodifying comonomer. It is to be noted that the intended color depthwith brilliancy, which has a color depth value Y rated as being higherthan class 7, cannot be obtained merely by a readily dyeable fiber whichhas been made at a ultra-high spinning speed; a fiber having micro-poresin the surface portion thereof which has been made by incorporatingultra-fine particles in a polymer and dissolving the ultra-fineparticles out from the polymer fiber after fiber-spinning; a fiber whichhas been rendered readily dyeable by treating with a metal sulfonate;and a fiber which has been heat-treated under relaxed conditions suchthat the non-crystalline regions are relaxed. Preferably, the dyedpolyester fabric of the invention is made from polyester fibers whereinthe degree of molecular orientation in the non-crystalline regions isnegligible and similar to that found in undrawn fibers which are usuallyof no practical use.

However, the above-mentioned polyester fibers possessing an extremelyreduced degree of molecular orientation in the non-crystalline regionsare very easily elongated by an external force and have a very poormechanical strength. Therefore, these polyester fibers are usedpreferably in combination with reinforcing highly oriented polyesterfibers to provide a yarn having a practically acceptable mechanicalstrength.

The highly oriented polyester fibers exhibit a poor color depth, whendyed. Therefore, to provide a yarn exhibiting a good color depth andhaving a practically acceptable mechanical strength, a composite yarnhaving a double-layer structure is advantageously used which is, asillustrated in FIG. 8A, composed of a core of reinforcing highlyoriented fibers (8) and a surface layer of fibers having a poormechanical strength but exhibiting an enhanced color depth (7). Themechanical strength of the yarn is predominantly dependent upon thereinforcing core fibers (8) and the deeply colored appearance of a dyedyarn is solely dependent upon the sheath fibers (7) exhibiting a goodcolor depth. This composite yarn is advantageously made from sheathfibers having a length of l₂ and reinforcing core fibers (FIG. 8B)having a length of l₁ wherein l₂ and l₁ satisfy the requirement:Δl×100≧5% wherein Δl=(l₂ -l₁)/l₁. To bear the external force applied tothe yarn by the reinforcing core fibers (8), the fibers (8) shouldpreferably have an elongation which is not larger than 50% and notlarger than two-thirds and, more preferably, not larger than one half ofthe elongation of the sheath fibers (7) exhibiting a good color depth.For the same purpose, the reinforcing core fibers (8) should preferablyhave a tenacity, expressed per denier, which is at least 1.5 times and,more preferably, at least 2 times that of the sheath fibers.

It is also important to select dyes for dyeing the yarn or the wovenfabric. As hereinbefore explained, in the deeply dyed polyester fabricof the invention, dye molecules are distributed in a random manner suchthat the molecules are oriented in all directions as illustrated in FIG.6, whereby all vibrating planes of natural light can be absorbed, andthus, undesirable light-brownish coloration is minimized and a brilliantand deep color is developed. However, light absorption in one directionis relatively weak as compared with the light absorption in which all ofthe dye molecules are oriented as illustrated in FIG. 7. Further, thecolor depth greatly varies depending upon the particular dye used. Morespecifically, dyes having conjugated double bonds as many as possible inthe molecule exhibit an enhanced light absorption and give a very deepcolor. That is, the intended color depth is obtained by the combined useof the fiber having an extremely reduced molecular orientation in thenon-crystalline regions and the dye having many conjugated double bondsin the molecule. In general, the higher the molecular weight of a dye,the more the conjugated double bonds in the dye molecule. Therefore, adye having a large molecular weight is preferably used in the presentinvention. It should be noted, however, that a dye having a highmolecular weight is readily oriented by the orientation of the polymermolecule of a fiber, when the dye is absorbed by the fiber. Therefore,the degree of molecular orientation in the non-crystalline regions ofthe polymer should be minimized. Dyes having a molecular weight of atleast 380 are preferable and, as dyes having a such a high molecularweight, there can be mentioned, for example, those which appearhereinafter in Table 2.

In the present invention, the difference (ΔX) between the lighttransmittance of polarized light vibrating perpendicular to the fiberaxis and the light transmittance of polarized light vibrating parallelto the fiber axis is an important measure for the fabrication of thedeeply dyed polyester fabric. However, if both of the two lighttransmittances are almost zero, i.e., the color is too dark, or if bothof the two transmittances are close to 100%, i.e., the color is toolight, then the dyed polyester fabric having the intended color depthcannot be obtained. Therefore, the lightness index L* value must be in alimited range which is from 25 to 65.

The dyeing procedure for the polyester fabric will be described in thefollowing.

The gray fabric is subjected to scouring and is then dyed. The dyeingmachine used is not particularly limited, and those which are widelyused for dyeing conventional polyester fabrics can be used. However, adyeing machine of the type wherein a dyeing bath is circulated ispreferable for dyeing the fabric woven from the yarns composed ofreinforcing core fibers and deeply dyeable sheath fibers. Usually, thegray fabric is dipped in a dyeing bath at a bath ratio of 1:5 to 1:50o.w.f., the temperature is elevated in 15 to 60 minutes to apredetermined dyeing temperature which is at least 120° C., and thedyeing bath is maintained at that temperature for 15 to 90 minutes.Preferably, the temperature elevation is effected gradually over aperiod of 45 to 60 minutes, and the dyeing is effected at a temperatureof at least 130° C. for a period of at least 45 minutes. The amount ofdye used is determined depending upon the intended degree of colordepth.

The above-mentioned deeply dyeable polyester yarns used for the deeplydyed fabric are costly in the production and troublesome to handle.Therefore, the deeply dyeable yarns can be woven in combination withother yarns into a mixed woven fabric from an economical viewpoint. Inthe fabrication of the mixed woven fabric, it is preferable that thedeeply dyeable yarns are of a larger crimp, i.e., are curved with alarger radius of curvature at the crossing points of the warps and thewefts than that of the other yarns so that the deeply dyeable yarns areexposed to a great extent to enhance the development of a deep colorwith brilliancy. Such a mixed woven fabric is advantageously made byweaving warps composed of the deeply dyeable polyester yarns and weftscomposed of the other yarns in a manner that the warp is overfed at arelaxing or finish setting step so as to possess larger crimps. Forexample, the warp curvature and the weft curvature are at least 20% andnot larger than 7%, respectively. Further, the deeply dyeable polyesterfiber preferably occupy at least 50%, more preferably at least 55 %,based on the weight of the fabric.

The fabric of the invention can be a crepe fabric which is woven from ahard twist yarn and has crinkled surfaces. The following problems shouldbe noted which are encountered when a crepe fabric is manufactured asthe deeply dyed fabric of the invention. That is, first, a hard twistyarn has a rough surface and exhibits an enhanced diffused reflectionwhich leads to reduction of color depth, and secondly, a yarn composedof fibers having little or no orientation in the non-crystalline regionsdoes not exhibit a good crepe effect. These problems can be solved byusing as the weft a hard twist yarn having, for example, at least 1,000twists per meter, which is made of a yarn capable of being easily madeinto a hard twist yarn, and using as the warp a deeply dyeable polyesteryarn in a manner such that weave crimps of the warp are larger thanthose of the weft and thus the warp is much more exposed on the surfaceof the woven fabric.

Cellulosic fibers such as acetate rayon and viscose rayon have a muchbetter color depth than conventional polyester fibers, although inferiorto natural silk. However, these cellulosic fibers have defects such thatfabrics thereof are readily wrinkled and shrunk when washed. Therefore,these fibers are used usually in combination with polyester fibers forweaving into fabrics. But, conventional polyester fibers and cellulosicfibers have a color depth greatly different from each other, and, amixed fabric woven therefrom has a poor color depth because the colordepth of the conventional polyester fibers offsets that of thecellulosic fibers.

In contrast, when cellulosic fibers and deeply dyeable polyester fibersare woven into a fabric, the resulting mixed fabric is characterized asexhibiting an excellent and matched color depth and possessing goodfeeling due to the cellulosic fibers and good functions due to thepolyester fibers. The procedure by which the mixed fabric is woven fromthe cellulosic fibers and the polyester fibers is not particularlylimited. For example, the cellulosic fibers and the polyester fibers arespun into a blended yarn, or the cellulosic yarn and the polyester yarnare interlaced, twined or twisted each other into a yarn, and theresulting yarn is woven into a fabric. Alternatively, the cellulosicyarn and the polyester yarn are woven together into a mixed fabric byusing one of the two kinds of yarns as the warp and the other as theweft. It is preferable that the deeply dyeable polyester yarn as thewarp and the cellulosic yarn as the weft are woven into a mixed fabricin a manner such that weave crimps of the warp are larger than those ofthe weft. Thus, a visually and sensuously excellent mixed fabric can beobtained which has a good color depth due to the warp and good drape andfeeling due to the weft.

The color depth of the deeply dyed fabric of the invention is mostconspicuous when the polyester yarn used is in the form of a flatfilament yarn composed of straight filaments, but a somewhat similareffect is obtained even when the polyester yarn used is composed ofcrimped or looped fibers or a hard twist yarn so as to impart to thefabric better feeling, heat insulation and stretchability. Further, evenwhen the polyester yarn used is a spun yarn made of staple fibers, asomewhat similar color depth can be obtained although diffusedreflection occurs to some extent due to the fluff and disordered fibersof the spun yarn.

In the case of warp or weft knitted fabrics, the deeply dyed mixedfabric can be made, for example, by knitting the deeply dyeablepolyester yarn for the warp or weft knitted fabrics, or knitting thedeeply dyeable polyester yarn as the weft or warp in the course ofpreparation of warp or weft knitted fabrics, respectively, of the otheryarns.

The polyester fiber used in the invention is not particularly limited,and may have either a round section or a polygonal section. Thepolyester fiber having a polygonal section exhibits not only a goodcolor depth but also a good luster. Ordinary polyester fibers having aporous structure and extremely fine polyester fibers exhibit diffusedreflection, but, if a good color depth is given in accordance with theinvention, these polyester fibers would exhibit an enhanced color depth.

The present invention can be applied to extremely fine polyester fibers.Recently, extremely fine polyester fibers are rated high because thesegive fabrics of a good and new touch. But, the conventional fabrics ofextremely fine polyester fibers exhibit enhanced diffused reflection,and hence, have a light brownish color and a poor color depth. If a goodcolor depth is given to extremely fine polyester fibers having athickness below 1 denier, especially below 0.6 denier, in accordancewith the present invention, the resulting fabrics exhibit a specialcolor depth which could not be obtained with the conventional fabrics ofextremely fine fibers, as well as a good touch. Thus, the polyesterfabrics of the invention made of extremely fine fibers are of asensuously and visually high grade.

EXAMPLES

The invention will now be described by the following examples.

Parameters used in the examples were determined as follows.

Light Transmittances X.sup.[, X⊥

Sample fibers are placed one by one in parallel on a slide glass,iodobenzene is dropped on the sample fibers and the fibers are coveredwith a covering glass sheet. Light transmittances are measured by usinga polarization microspectroscope photometer "model DSP-SP-100-PO"supplied by Olympus Optical Co. A beam of polarized incident lighthaving a diameter of 2 μm is projected to the fibers so that the beam isparallel to the fiber axis, and spectral transmittance is measured inthe visible wavelength region of 400 to 700 nm, wherein thetransmittance at the area where the fibers are not present is thereference transmittance. The transmittance at a wavelength correspondingto the minimum transmittance is X.sup.[ (%). Similarly, a beam ofpolarized incident light is projected to the fibers so that the beam isperpendicular to the fiber axis, and the transmittance X⊥ (%) at awavelength corresponding to the minimum transmittance in the visiblewavelength region of 400 to 700 μm is measured.

Degree of Orientation of Entire Fiber (Birefringence Δn)

Birefringence Δn is determined by using a polarization electronmicroscope according to the Senarmont method.

Degree of Crystallinity χc

X-ray diffraction pattern was prepared by using an X-ray generatorRAD-IIIA supplied by Rigaku Electric Co. combined with a counter PSDCsystem, and by employing 35 kv×10 mA, a CuKα-line Ni filter, and adivergent slit of 1 mm φ.

While the fibers are rotated in a plane perpendicular to the X-ray beam,the total diffused reflection is determined on the crystalline region(in the case of polyester filaments, the determination is carried out at2θ=10° to 40°). Similarly, the total diffused reflection is determinedon the non-crystalline region. The degree of crystallinity χc iscalculated according to the following equation. ##EQU1##

Degree of Crystal Orientation Fc

Degree of crystal orientation is calculated from the following equation:

    F.sub.c (%)=[(180°-H°)/180°]×100

wherein H° is the half-value width of an X-ray diffraction pattern inthe (110) plane. Note, in an X-ray diffraction pattern in the (100)plane, the spot is not always concentrated on the equator andoccasionally separated into upper and lower sides of the equator.Therefore, the diffraction in the (110) plane was employed.

Degree of Non-crystalline Orientation Δna

Degree of non-crystalline orientation Δna is calculated from thefollowing equation

    Δna=(Δn-0.212Fcχc)/(1-χc).

Lightness Index L*

The ligntness index L* is defined by Commission Internationale del'Eclairage (CIE) and determined according to JIS-Z-8729-1980. Thelarger the lightness index L* value, the lighter the fiber color. Thesmaller the L* value, the darker and deeper the fiber color. Thelightness index L* value is measured by using a spectrophotomerterMacbeth® Color Eye.

Comparative Example 1

This comparative example corresponds to Run No. 1 in Table 1.

Polyethylene terephthalate was melt-spun into filaments at a spinningspeed of 1,500 m/min. The filaments were drawn three times the originallength wherein a part of the filaments were passed on a heated platemaintained at 160° C. and the other part thereof were not passed on aheated plate, whereby two kinds of drawn filaments were prepared, eachkind being composed of 18 filaments with 30 denier in total. The twokinds of filaments having different shrinkability were mix-spun into asilky mixed polyester filament yarn composed of 36 filaments with 60denier in total.

A gray fabric was woven from the silky mixed polyester filament yarn asboth a warp and a weft. The gray fabric was scoured with boiling waterusing a surfactant under a relaxed condition and then set at 180° C.Thereafter the fabric was dyed under the following conditions.

Dyeing temperature: temperature was elevated at a rate of 2° C./rainfrom normal temperature, and dyeing was carried out at 130° C. for 60min.

Dyestuff and amount: C. I. Disperse Red 92 with a molecular weight of496; 5% owf

Dyeing auxiliaries: Disper VG 0.5 g/l+acetic acid 0.2 ml/l

Bath ratio: 1:50

After dyeing, the dyed fabric was washed under a reducing condition,dried and then set at 160° C. The resultant dyed fabric was silky, andexhibited a lightness index L* of 39.8, and a color depth Y of class 1as expressed by 10 rating visual organoleptic test, provided that thecolor depth Y of silk is rated as class 7.

Dyed fibers were collected from the surface layer portion of the dyedfabric and the light transmittances X.sup.[ and X⊥ were determined. Thespectrum of polarized transmitted light in the direction parallel to thefiber axis and that in the direction perpendicular to the fiber axis inthe visible light wavelength region (400 to 700 nm) are shown as A andB, respectively, in FIG. 9. The maximum absorption wavelength λ₀ (i.e.,a wavelength corresponding to the minimum transmittance) was 520 nm. Atthe wavelength of 520 nm, the light transmittance X.sup.[ of A was 2%and the light transmittance X⊥ of B was 32%. Thus, ΔX (=X⊥-X.sup.[) was30%.

Comparative Example 2

This comparative example corresponds to Run No. 2 in Table 1.

Ultrafine particles of a water-soluble inorganic substance having adiameter not larger than 0.1 μm were uniformly dispersed in polyethyleneterephthalate in an amount of 3% by weight. The polyethyleneterephthalate was then melt-spun into filaments at a spinning speed of1,200 m/rain by an ordinary spinning procedure and the filaments weredrawn 3.6 times the original length to prepare a filament yarn composedof 36 filaments with 75 denier in total. A gray fabric was woven fromthe filament yarn as both a warp and a weft. The fabric was scoured, setat 180° C., and then treated with an aqueous sodium hydroxide solutionhaving a concentration of 3% by weight at 100° C. for 20 minutes wherebythe ultrafine particles of inorganic substance were dissolved andremoved from the fibers. The thus-treated fabric was characterized asbeing composed of fibers having a rough surface with numberlessultrafine projections so that incident light was absorbed by theultrafine projections. The fabric was dyed under the same conditions asemployed in Comparative Example 1.

Light transmittances X.sup.[ and X⊥ were determined on dyed fiberscollected from the surface layer portion of the dyed fabric. Thespectrum of transmitted light in the direction parallel to the fiberaxis and that in the direction perpendicular to the fiber axis in thevisible light wavelength region are shown as A and B, respectively, inFIG. 10. The maximum absorption wavelength λ₀ was 520 nm, namely, thesame as that in Comparative Example 1 because of the same dyestuff. Thedifference in polarized light transmittance ΔX (=X⊥-X.sup.[) wasrelatively small, i.e., 27%. But, the dyed fabric had a color depth Y ofclass 2.

Comparative Example 3

This comparative example corresponds to Run No. 3 in Table 1.

Polyethylene terephthalate having copolymerized therewith 5% by mole of5-sodium-sulfoisophthalic acid was melt-spun into filaments at aspinning speed of 2,500 m/min and the filaments were drawn 2.0 times theoriginal length by an ordinary procedure to prepare a filament yarnhaving an improved dyeability composed of 24 filaments with 100 denierin total.

A gray fabric was woven from the filament yarn as both a warp and aweft. The fabric was scoured and dyed under the same conditions asemployed in Comparative Example 1 except that the dyeing temperature waschanged to 100° C.

Light transmittances X⊥ and X.sup.[ it were determined on dyed fiberscollected from the surface layer portion of the dyed fabric. Thespectrum of transmitted light in the direction parallel to the fiberaxis and that in the direction perpendicular to the fiber axis in thevisible light wavelength region are shown as A and B, respectively, inFIG. 11. The difference in polarized light transmittance ΔX was 23%. Thecolor depth Y of the dyed fabric was class 3.

For comparison, the above-mentioned procedure was repeated wherein thedyeing temperature was raised to 130° C., but the results were ratherunsatisfactory as compared with the above results.

Comparative Example 4

This comparative example corresponds to Run No. 4 in Table 1.

Polyethylene terephthalate was melt-spun into filaments at a spinningspeed of 3,500 m/min, and the filaments were drawn 1.5 times theoriginal length and heat-treated under a relaxed condition using aheater maintained at 180° C. to prepare a filament yarn composed of 24filaments with 50 denier in total, which was characterized in that thenon-crystalline region was self-elongatable. The filament yarn was mixspun with a highly shrinkable polyester filament yarn composed of 12filaments with 30 denier in total to prepare a mixed yarn of filamentshaving different shrinkabilities (36 filaments with 80 denier in total).

A gray fabric was woven from the mixed filament yarn as both a warp anda weft. The fabric was scoured and dyed under the same conditions asemployed in Comparative Example 1.

The resultant dyed fabric was soft and had a good drapability and touch,which is classified into a fabric of a new synthetic fiber. Lighttransmittances X⊥ and X.sup.[ were determined on dyed fibers collectedfrom the surface layer portion of the dyed fabric. The spectrum oftransmitted light in the direction parallel to the fiber axis and thatin the direction perpendicular to the fiber axis in the visible lightwavelength region are shown as A and B, respectively, in FIG. 12. Thedifference in polarized light transmittance ΔX was 17%. The color depthY of the dyed fabric was class 5, and thus, poor as compared with thatof silk.

Comparative Example 5

This comparative example corresponds to Run No. 5 in Table 1.

Polyethylene terephthalate was melt-spun into filaments at a spinningspeed of 7,000 m/min so as to obtain filaments exhibiting a very highrate of dye absorption, whereby a deeply dyeable filament yarn composedof 24 filaments with 50 denier in total.

A gray fabric was woven from the filament yarn as both a warp and aweft. The fabric was scoured and dyed under the same conditions asemployed in Comparative Example 1 except that the dyeing temperature waschanged to 110° C.

The resultant fabric had a soft touch which was characteristic tofilaments spun at a ultra-high spinning speed. The fabric could be dyedat 110° C. and exhibited a color index L* of 38.5, but the coloring wasnot deep, namely the color depth Y value was class 5. Lighttransmittances X⊥ and X.sup.[ were determined on dyed fibers collectedfrom the surface layer portion of the dyed fabric. The spectrum oftransmitted light in the direction parallel to the fiber axis and thatin the direction perpendicular to the fiber axis in the visible lightwavelength region are shown as A and B, respectively, in FIG. 13. Thedifference in polarized light transmittance ΔX was 14%.

For comparison, the above-mentioned procedure was repeated wherein thedyeing temperature was raised to 130° C., but the results were similarlyunsatisfactory.

Example 1

This example corresponds to Run No. 6 in Table 1.

Polyethylene terephthalate was melt-spun into filaments at a spinningspeed of 2,500 m/min. The filaments were heat-treated at 220° C. for0.05 second as they were in an undrawn state to prepare an undrawnpolyester filament yarn composed of 24 filaments with 30 denier intotal. The filament yarn was mix-spun with a highly shrinkable polyesterfilament yarn having an elongation of 25% composed of 12 filaments with30 defiler in total, to prepare a polyester filament yarn composed of 36filaments with 60 denier in total.

A gray fabric was woven from the polyester filament yarn as both a warpand a weft. The gray fabric was scoured and dyed under the sameconditions employed in Comparative Example 1.

The dyed fabric was bulky and was composed of two types of filamentshaving different lengths l₃ and l₂ wherein the difference in % of (l₂-l₁) was 15%. Light transmittances X⊥ and X.sup.[ were determined ondyed fibers collected from the surface layer portion of the dyed fabric.The spectrum of transmitted light in the direction parallel to the fiberaxis and that in the direction perpendicular to the fiber axis in thevisible light wavelength region are shown as A and B, respectively, inFIG. 14. The difference in polarized light transmittance ΔX was only 5%.The dyed fabric exhibited a color depth Y of class 9. Namely, the fabricwas more deeply and brilliantly dyed than silk, and far more deeply andbrilliantly dyed than conventional synthetic fibers.

Example 2

This example corresponds to Run No. 7 in Table 1.

Polyethylene terephthalate was melt-spun into filaments at a spinningspeed of 2,800 m/min. The filaments were heat-treated by a heatermaintained at 240° C. as they were in an undrawn shake under relaxedconditions such that the overfeed ratio was 15%, whereby an undrawnpolyester filament yarn was obtained which was composed of 24 filamentswith 50 denier in total and characterized in that the non-crystallineregion was completely non-oriented. The filament yarn was mix-spun witha highly shrinkable polyester filament yarn having an elongation of 27%composed of 10 filaments with 40 denier in total, to prepare a polyesterfilament yarn composed of 34 filaments with 90 denier in total.

A gray fabric was woven from the polyester filament yarn as both a warpand a weft. The gray fabric was scoured and dyed under the sameconditions employed in Comparative Example 1.

The dyed fabric was bulky and soft and had a good drapability. The dyedfabric had an appearance similar to those of new synthetic fibers, andwas composed of two types of filaments having different lengths l₁ andl₂, wherein the difference of (l₂ -l₁) was 18%. The dyed fabricexhibited a color depth Y of class 10, namely, the fabric was much moredeeply and brilliantly dyed than silk. Light transmittances X⊥ andX.sup.[ were determined on dyed fibers collected from the surface layerportion of the dyed fabric. The speckrum of transmitted light in thedirection parallel to the fiber axis and that in the directionperpendicular to the fiber axis in the visible light wavelength regionare shown as A and B, respectively, in FIG. 15. The difference inpolarized light transmittance ΔX was only 3%, namely, the transmittancewas almost isotropic.

Example 3

Dyed fabrics of different colors were made by substantially the sameprocedure as described in Example 1 wherein the dyestuffs listed inTable 2 were used. The results are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                                           Mole-   Spectrum of                                                           cular   transmitted                                                                            ΔX                                                                           Y                                    Color  Dyestuff    weight  light    (%)  (class)                              ______________________________________                                        Scarlet                                                                              C.I.Disperse                                                                              398     FIG. 16  8    8                                           Red 356                                                                Orange C.I.Disperse                                                                              360     FIG. 17  6    7                                           Red 356                                                                       (60%) +                                                                       Yellow 23                                                                     (40%)                                                                  Green  C.I.Disperse                                                                              402     FIG. 18  4    10                                          Blue 354                                                                      (50%) +                                                                       Yellow 23                                                                     (60%)                                                                  Cobalt C.I.Disperse                                                                              461     FIG. 19  7    9                                    green  Blue 354                                                                      (80%) +                                                                       Yellow 23                                                                     (20%)                                                                  Sky blue                                                                             C.I.Disperse                                                                              501     FIG. 20  6    7                                           Blue 354                                                               Dark   C.I.Disperse                                                                              404     FIG. 21  8    8                                    blue   Blue 165                                                               Violet C.I.Red     459     FIG. 22  9    8                                           92 (50%) +                                                                    C.I. Violet                                                                   26 (50%)                                                               ______________________________________                                    

As seen from the examples of the invention, the requirement ofdifference in polarized light transmittance ΔX≦10% and the effect ofcolor depth Y≧7 are satisfied in all of the colors.

For comparison, dyed fabrics of different colors were made bysubstantially the same procedure as described in Comparative Example 1and by using the same dyestuffs listed in Table 2. The results are shownin Table 3.

As seen from Table 3, the difference in polarized light transmittance ΔXexceeds 10 and the color depth Y is only in the range of class 1 toclass 3 in all of the colors.

                  TABLE 3                                                         ______________________________________                                                  Spectrum of                                                                   transmitted    ΔX                                                                             Y                                             Color     light          (%)    (class)                                       ______________________________________                                        Scarlet   FIG. 23        15     1                                             Orange    FIG. 24        16     1                                             Green     FIG. 25        13     2                                             Cobalt    FIG. 26        19     1                                             green                                                                         Sky blue  FIG. 27        11     3                                             Dark      FIG. 28        12     2                                             blue                                                                          Violet    FIG. 29        15     1                                             ______________________________________                                    

As seen from Table 3, the difference in polarized light transmittance ΔXexceeds 10 and the color depth Y is only in the range of class 1 toclass 3 in all of the colors.

Example 4l

Using the mix spun polyesher filament yarn (34 filaments with 90 defilerin total) as weft, and a hard twist yarn as a warp which was prepared bytwisting an ordinary drawn polyester filament yarn (72 filaments with 75denier in total) at 2,000 twists per meter, a gray fabric was made. Thegray fabric was scoured and dyed under the same conditions as thoseemployed in Comparative Example 1 except that, when scoured and set, thefabric was overfed in its warp direction so as to permit the maximumshrinkage to occur, but only a minor shrinkage was permitted to occur inthe weft direction. The resultant dyed fabric exhibited a crimppercentage of 26% in the warp direction and a crimp percentage of 3% inthe weft direction, namely, was corrugated only in the warp direction.

Although an ordinary polyester filament yarn was used as the weft, onlythe warp was predominantly exposed on the surface, and therefore, thefabric exhibited a color depth Y value of class 8. The difference inpolarized light transmittance ΔX as measured on dyed fibers collectedfrom the surface layer portion of the dyed warp was only 3%, and that asmeasured on dyed fibers collected from the surface portion of the weftwhich was not exposed was 35%.

Example 5

Using the mix spun polyester filament yarn (34 filaments with 90 denierin total) as weft, and a heat-resistant acetate filament yarn (20filaments with 70 denier in total), a gray fabric was made. The grayfabric was scoured and dyed under the same conditions as those employedin Example 4 wherein the fabric was overfed in its warp direction so asto permit the maximum shrinkage to occur, but only a minor shrinkage waspermitted to occur in the weft direction. The resultant dyed fabricexhibited a crimp percentage of 22% in the warp direction and a crimppercentage of 5% in the weft direction. The fabric exhibited a colordepth Y value of class 9.

Example 6

Polyethylene terephthalate was melt spun at a spinning speed of 2,900m/min to prepare a filament yarn composed of 144 ultra-fine filamentswith 72 denier in total (i.e., single filament=0.4 denier). The filamentyarn was heat-treated at a high temperature of 235° C. under relaxedconditions such that the overfeed ratio was 10%, without drawing toprepare a filament yarn characterized in that the non-crystallineportion is oriented only to a negligible extent.

A gray fabric was woven from the filament yarn as both a warp and aweft. The fabric was scoured and dyed under the same conditions as thoseemployed in Comparative Example 1, and was then subjected to a buffingtreatment.

Although the fabric is composed of ultra-fine filaments, the fabricexhibited a color depth Y of class 8. It would be noted that ultra-finefilaments exhibit a large irregular reflection and thus their colors areneither bright nor deep, but are tinged with somewhat light brownishcolor. Therefore, the fabric of this example is distinguished fromconventional fabrics composed of ultra-fine filaments which arepopularly called as new synthetic fibers.

Example 7

A cationic dye-dyeable polyethylene terephthalate was melt spun into afilament yarn composed of 12 filaments with 30 denier in total whereinthe melt-spinning was carried out at an ultra-high draft ratio, i.e., adraft ratio of 200,000 times by using a spinneret with orifices having avery large diameter, which offers a striking contrast with theconventional melt spinning employing a draft ratio of about 100 or so.Thus, the filament yarn characterized as exhibiting an orientation onlyto a minor extent was obtained directly from a polyester having noorientation.

The filament yarn was knitted into a tricot fabric by using a 36 gaugetricot machine without drawing the filament yarn. The fabric wasscoured, dyed with 5% owf of C.I.Disperse Red 92 at 120° C., and thenset at 160° C.

Light transmittances X⊥ and X.sup.[ were determined on dyed fiberscollected from the surface layer portion of the dyed fabric. Thespectrum of transmitted light in the direction parallel to the fiberaxis and that in the direction perpendicular to the fiber axis in thevisible light wavelength region are shown as A and B, respectively, inFIG. 30. The difference in polarized light transmittance ΔX was only 8%.The tricot fabric exhibited a color depth y of class 7, which is similarto that of silk.

Example 8

A weft knitted fabric was made by feeding two of the mix spun polyesterfilament yarn to a 16 gauge interlock tubular knitting machine. The weftknitted fabric was scoured and dyed under the same conditions asemployed in Comparative Example 1. The color was brilliant and deep andthe color depth Y was class 9.

As a modification of the weft knitted fabric, a weft knitted fabric wasmade in a similar manner wherein a warp composed of an ordinarypolyester filament yarn (24 filaments with 50 denier in total) wasinserted into the weft knitting system. The ordinary polyester filamentyarn was embedded as a core in the weft knitted fabric, and thus, onlythe weft was exposed on the surface of the fabric. Therefore, a dyedproduct of the modified weft knitted fabric had a similarly brilliantand deep color.

Industrial Applicability

The dyed polyester fabric of the invention is superior in feeling andcolor shade to natural fiber fabrics.

It is to be noted that a polyester conjugate fiber yarn composed offilaments having greatly different shrinkages, which are popularlycalled as new synthetic fibers, offers a fabric having bulkiness,drapability and touch which are superior to those of silk, but the dyedfabric does not meet the consumers' demand in the color depth. Thisproblem can be solved by the dyed fabric of the invention, which hasbrilliant and deep color.

The dyed fabric of the invention is useful as scarves, dresses, blouses,jackets, skirts, pants, coats, blouson, curtains and pet covers.

We claim:
 1. A deeply dyed polyester fabric composed of warps and wefts,which are dyed with a lightness index L* value of 25 to 65; fibers atleast in the surface layer portion of either or both of the warps andthe wefts exhibiting a light transmittance that the difference (ΔX in %)between the light transmittance (X⊥ in %) of polarized light vibratingperpendicular to the fiber axis at a wavelength of the maximumabsorption and the light transmittance (X.sup.[ in %) of polarized lightvibrating parallel to the fiber axis at the same wavelength is notlarger than 10%.
 2. A deeply dyed polyester fabric according to claim 1,wherein either or both of the warps and the wefts having the fiberssatisfying said transmittance requirements at least in the surface layerportion thereof is composed of core fibers and surface layer fibers; andthe surface layer fibers have a length at least 5% longer than the corefibers.
 3. A deeply dyed polyester fabric according to claim 2, whereinthe core fibers have an elongation which is not larger than 40% and notlarger than 2/3 of the elongation of the surface layer fibers; and thecore fibers have a strength per denier at least 1.5 times the strengthper denier of the surface layer fibers.
 4. A deeply dyed polyesterfabric according to any of claims 1 to 3, wherein the warps have thefibers satisfying said transmittance requirements at least in thesurface layer portion thereof, and the wefts are composed of polyesterfibers or other fibers, which are different from the surface layerfibers of the warps; and the warps in the fabric are woven at a crimppercentage larger than that of the wefts in time fabric.
 5. A deeplydyed polyester fabric according to claim 4, wherein the wefts are a lardtwist yarn having at least 1,000 twists per meter.
 6. A deeply dyedpolyester fabric according to claim 4, wherein the warps are containedin an amount of at least 55% by weight based on the weight of thefabric.
 7. A deeply dyed polyester fabric according to claim 4, which isa mixed woven fabric wherein the wefts are composed of a cellulosicfiber.
 8. A deeply dyed polyester fabric according to claim 1 to 3,wherein either of both of the warps and wefts having the fiberssatisfying said transmittance requirements at least in the surface layerportion thereof are composed of ultra-fine fibers having a thickness notlarger than 1 denier.
 9. A deeply dyed polyester fabric according claims1 to 3, which is dyed with a dyestuff having a molecular weight of atleast 380.